Recent evolutions of imagery in fluid mechanics: From standard tomographic visualization to 3D volumic velocimetry

The recent evolutions of the optical analysis of three-dimensional (3D) flows by means of light scattering and quantitative imagery are presented. In order to remove the intrinsic ambiguity of the wellknown tomographic methods (how to obtain 3D information by using a 2D plane illumination?), the efficiency of polychromatic lightings is shown: the basic idea is to code the third dimension by the wavelength.Different approaches are described: discrete or continuous analysis, sequential or simultaneous recordings, and measurement of two or three velocity components (2C or 3C techniques).The most recent 3D velocimetry method using a rainbow lighting process (RVV— Rainbow Volumic Velocimetry) is presented. The main qualities and limitations of these different methods are discussed.